How many opioid receptors are there?
It is important to know that opioid receptors are a group of G protein-coupled receptors with opioids as ligand. There are four major subtypes of opioid receptors: delta (?), kappa (?), mu (?) and Nociceptin receptor. It is important to know that the receptors were named using the first letter of the first ligand that was found to bind to them. Moreover, it is imperative to know that opiate receptors are distributed widely in the brain. They are also found in the spinal cord and digestive tract.